16,330 research outputs found
Quantifying the Effect of Non-Larmor Motion of Electrons on the Pressure Tensor
In space plasma, various effects of magnetic reconnection and turbulence
cause the electron motion to significantly deviate from their Larmor orbits.
Collectively these orbits affect the electron velocity distribution function
and lead to the appearance of the "non-gyrotropic" elements in the pressure
tensor. Quantification of this effect has important applications in space and
laboratory plasma, one of which is tracing the electron diffusion region (EDR)
of magnetic reconnection in space observations. Three different measures of
agyrotropy of pressure tensor have previously been proposed, namely,
, and . The multitude of contradictory measures has
caused confusion within the community. We revisit the problem by considering
the basic properties an agyrotropy measure should have. We show that
, and are all defined based on the sum of the
principle minors (i.e. the rotation invariant ) of the pressure tensor. We
discuss in detail the problems of -based measures and explain why they may
produce ambiguous and biased results. We introduce a new measure
constructed based on the determinant of the pressure tensor (i.e. the rotation
invariant ) which does not suffer from the problems of -based
measures. We compare with other measures in 2 and 3-dimension
particle-in-cell magnetic reconnection simulations, and show that can
effectively trace the EDR of reconnection in both Harris and force-free current
sheets. On the other hand, does not show prominent peaks in
the EDR and part of the separatrix in the force-free reconnection simulations,
demonstrating that does not measure all the non-gyrotropic
effects in this case, and is not suitable for studying magnetic reconnection in
more general situations other than Harris sheet reconnection.Comment: accepted by Phys. of Plasm
Future directions for tourism at the Houtman Abrolhos Islands - draft for public comment
This paper discusses the constraints on tourism in the Abrolhos and key management strategies of the draft tourism plan. Discusses facilities required and recommending a broadening of air services to allow their use for tourism, establishment of boat moorings for commercial tourist operators, public moorings may be installed and rented for use by private boats, upgrading of facilites Dransfield House on Beacon Island, could be used as an interpretive centre
Management plan for sustainable tourism at the Houtman Abrolhos Islands
The combination of unique species of fish, coral reefs and other invertebrates, historical shipwrecks and the commercially valuable Western rock lobster makes the Abrolhos a unique area of Western Australia. In recognition of this the Minister of Fisheries is releasing the plan \u27Management of Houtman Abrolhos System\u27, following a period of public consultation. The islands are becoming increasingly popular destination for tourists that are attracted to the diving, fishing, bird watching, maritime history and other features of the Abrolhos. The draft Management Plan for Sustainable Tourism in the Houtman Abolhos Islands has been developed to provide a framework within which tourism can be developed on the islands. The goal of the draft Management Plan for Sustainable Tourism at the Houtman Abrolhos Islands is to: Manage environmentally senstive nature-based tourism which is constent with the values of the Abrolhos System and provides appropriated access to the area for the community
Tidal instability in a rotating and differentially heated ellipsoidal shell
The stability of a rotating flow in a triaxial ellipsoidal shell with an
imposed temperature difference between inner and outer boundaries is studied
numerically. We demonstrate that (i) a stable temperature field encourages the
tidal instability, (ii) the tidal instability can grow on a convective flow,
which confirms its relevance to geo- and astrophysical contexts and (iii) its
growth rate decreases when the intensity of convection increases. Simple
scaling laws characterizing the evolution of the heat flux based on a
competition between viscous and thermal boundary layers are derived
analytically and verified numerically. Our results confirm that thermal and
tidal effects have to be simultaneously taken into account when studying
geophysical and astrophysical flows
Tubulin cofactors and Arl2 are cage-like chaperones that regulate the soluble αβ-tubulin pool for microtubule dynamics.
Microtubule dynamics and polarity stem from the polymerization of αβ-tubulin heterodimers. Five conserved tubulin cofactors/chaperones and the Arl2 GTPase regulate α- and β-tubulin assembly into heterodimers and maintain the soluble tubulin pool in the cytoplasm, but their physical mechanisms are unknown. Here, we reconstitute a core tubulin chaperone consisting of tubulin cofactors TBCD, TBCE, and Arl2, and reveal a cage-like structure for regulating αβ-tubulin. Biochemical assays and electron microscopy structures of multiple intermediates show the sequential binding of αβ-tubulin dimer followed by tubulin cofactor TBCC onto this chaperone, forming a ternary complex in which Arl2 GTP hydrolysis is activated to alter αβ-tubulin conformation. A GTP-state locked Arl2 mutant inhibits ternary complex dissociation in vitro and causes severe defects in microtubule dynamics in vivo. Our studies suggest a revised paradigm for tubulin cofactors and Arl2 functions as a catalytic chaperone that regulates soluble αβ-tubulin assembly and maintenance to support microtubule dynamics
Non-radial motion and the NFW profile
The self-similar infall model (SSIM) is normally discussed in the context of
radial orbits in spherical symmetry. However it is possible to retain the
spherical symmetry while permitting the particles to move in Keplerian
ellipses, each having the squared angular momentum peculiar to their 'shell'.
The spherical 'shell', defined for example by the particles turning at a given
radius, then moves according to the radial equation of motion of a 'shell'
particle. The 'shell' itself has no physical existence except as an ensemble of
particles, but it is convenient to sometimes refer to the shells since it is
they that are followed by a shell code. In this note we find the distribution
of squared angular momentum as a function of radius that yields the NFW density
profile for the final dark matter halo. It transpires that this distribution is
amply motivated dimensionally. An effective 'lambda' spin parameter is roughly
constant over the shells. We also study the effects of angular momentum on the
relaxation of a dark matter system using a three dimensional representation of
the relaxed phase space.Comment: accepted for publication in Astronomy and Astrophysics. date
received: 31-03-03 date accepted: 10-06-0
Backscattered intensity profiles from horizontal Acoustic Doppler Current Profilers
River engineeringInnovative field and laboratory instrumentatio
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